The increasing popularity of portable electronic devices, such as notebook computers, mobile phones, digital still cameras and camcorders, has caused an increasing demand for rechargeable batteries, which include, but are not limited to, nickel-cadmium, nickel-metal hydride, lithium-ion, and lithium-polymer batteries.
It may be desirable for the portable electronic devices to be in-field rechargeable, which means that a battery can be recharged without removing the battery from a device or affecting the normal function of a device. When the external power source charges the battery and powers the system simultaneously, the charging current should be adjusted automatically to fulfill first the current requirement of the system.
There are two types of charging methods. One is switching mode, where the battery is charged through a periodically on/off switch. The other one is linear mode, where the battery is charged through a variable resistor. Switching mode charging has higher efficiency, but introduces more switching noise into the system due to the generation and use of an oscillation signal. In contrast, linear mode charging is cleaner at the cost of higher power dissipation.
Different devices may require different charging modes, or the same devices may require different charging modes under different conditions. Thus it is desirable to have a dual mode battery charger for portable electronic devices, and it should be configurable according to user requirements.
Different types of rechargeable batteries may require different charging phases under different conditions. For example, for a deeply discharged battery, a small wake-up charging current may be required to revive it. For a normally discharged battery, a large charging current may be required to achieve the highest charging speed. For an almost full battery, a tapering charging current may be required to keep the battery voltage at a constant level.
If the battery requires a large charging current to maximize the charging speed, a soft-start function may be desired to prevent a big inrush current flowing into the battery, which is realized by gradually increasing the charging current to its full scale.
A portable electronic device may be powered by multiple power sources, such as batteries, high power supplies, and restricted power supplies, which may be perturbed when the drawing current exceeds the predetermined maximum rating current. The high power supplies have the highest priority, the restricted power supplies have a medium priority, and the batteries have the lowest priority. If one of the high power supplies is present, it should charge the battery and power the system, regardless the presence of the restricted power supplies or batteries. If all of the high power supplies are not available and one of the restricted power supplies is available, this restricted power supply should be connected to the system power line using a soft-start procedure to limit the inrush current below its predetermined maximum rating current. When an over-current event occurs, the power input of the system should be switched from the restricted power supply to one of the batteries. Moreover, during any switching procedure, the system power integrity should be assured.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. Accordingly, it is intended that the claimed subject matter be viewed broadly, and be defined only as set forth in the accompanying claims.